TUAW posted a story that early 2009 iMacs with NVIDIA GeForce GT 130 GPU have a problem with kernel panics under Mountain Lion

Apparently Apple isn't too concerned with the issue, since the support community thread discussing it is now up to 14 pages long, with almost 200 replies. That thread was started by user David Portela almost a year ago, and a number of users have now spoken up about the issue. The issue can be traced to a new kernel extension that was released during the lifetime of Snow Leopard and has not been fixed. Many users note that the issue disappears when they are running versions of Windows on their iMacs via Boot Camp, so the Windows drivers apparently work on Apple hardware better than the Mac drivers do.